350 



Abstract — Rex sole iGlyptncephalus 

 zachirus) have a wide distribution 

 throughout the North Pacific, rang- 

 ing from central Baja California to 

 the western Bering Sea. Although rex 

 sole are an important species in the 

 commercial trawl fisheries off the U.S. 

 West Coast, knowledge of their repro- 

 ductive biology is limited to one study 

 off the Oregon coast where ovaries 

 were analyzed with gross anatomi- 

 cal methods. This study was initi- 

 ated to determine reproductive and 

 growth parameters specific to rex sole 

 in the Gulf of Alaska (GOA) stock. 

 Female rex sole (;7 = 594) ranging in 

 total length from 166 to 552 mm were 

 collected opportunistically around 

 Kodiak Island. Alaska, from Febru- 

 ary 2000 to October 2001. All ova- 

 ries were analyzed by using standard 

 histological criteria to determine the 

 maturity stage. Year-round sampling 

 of rex sole ovaries confirmed that rex 

 sole are batch spawners and have a 

 protracted spawning season in the 

 GOA that lasts at least eight months, 

 from October to May; the duration of 

 the spawning season and the months 

 of spawning activity are different 

 from those previously estimated. 

 Female rex sole in the GOA had 

 an estimated length at ?>()% maturity 

 (MLjq) of 352 mm, which is greater 

 than the previously estimated ML^p 

 at southern latitudes. The maximum 

 age of collected female rex sole was 29 

 years, and the estimated age at 50% 

 maturity (MAjg) in the GOA was 5.1 

 years. The von Bertalanffy growth 

 model for rex sole in the GOA was 

 significantly different from the previ- 

 ously estimated model for rex sole off 

 the Oregon coast. This study indicated 

 that there are higher growth rates 

 for rex sole in the GOA than off the 

 Oregon coast and that there are dif- 

 ferences in length at maturity and 

 similarity in age at maturity between 

 the two regions. 



Reproductive biology, spawning season, and growth 

 of female rex sole (Glyptocephalus zachirus) 

 in the Gulf of Alaska 



Alisa A. Abookire 



Kodiak Laboratory 



Alaska Fisheries Science Center 



National Marine Fisheries Service 



301 Research Court 



Kodiak, Alaska 99615 



Email. alisa.abookire(Snoaa gov 



Manuscript submitted 5 January 2005 

 to the Scientific Editor's Office. 



Manuscript approved for publication 



19 September 2005 by the Scientific Editor. 



Fish. 104:350-359 (20061. 



Rex sole (Glyptocephalus zachirus) 

 have a wide distribution throughout 

 the North Pacific, ranging from cen- 

 tral Baja California to the western 

 Bering Sea (Mecklenburg at al. 2002). 

 The rex sole population is made up 

 of several stocks that are managed 

 as four separate units: the U.S. West 

 Coast stock which includes waters off 

 the coasts of California, Oregon, and 

 Washington; the British Columbia 

 stock which is managed separately 

 by the Canadian government; the 

 Gulf of Alaska (GOA) stock; and the 

 Bering Sea stock (TurnockM. The U.S. 

 West Coast stock of rex sole provided a 

 steady and stable commercial fishery 

 in California between 1970 and 1989, 

 but landings began to decline in the 

 1990s (Quirollo and Dewees'). Rex 

 sole are managed as part of the "other 

 flatfish" category for both the West 

 Coast stock (Quirollo and Dewees-) 

 and the Bering Sea stock (Spencer 

 et al.3). 



Throughout its range, the largest 

 commercial harvest of rex sole oc- 

 curs in the GOA where rex sole are 

 one of the major commercial flatfish 

 species. Since 1988, the commercial 

 trawl fishery for flatfish in the GOA 

 has concentrated in the central Gulf 

 on the continental shelf and slope 

 east of Kodiak Island (DiCosimo and 

 KimbalH). Development of a man- 

 agement plan for the rex sole fishery 

 in the GOA has undergone several 

 phases. Prior to 1990, all flatfishes in 

 the GOA with the exception of Pacific 

 halibut {Hippoglossus stenolepis) were 

 managed as one assemblage. In 1990, 

 four flatfish categories were created 

 for stock assessment: shallow-water 



complex, deep-water complex (rex sole 

 included), flathead sole {Hippoglos- 

 soides elassodo?!), and arrowtooth 

 flounder [Atheresthes stomias). In 

 1993, rex sole were removed from the 

 deep-water complex and managed as 

 a separate species. 



In 2003, biomass estimates for rex 

 sole in the Gulf of Alaska totaled 

 99,950 metric tons (t), and the accept- 

 able biological catch (ABC ) was 9466 t 

 (Turnock et al.'^). Annual commercial 

 landings for GOA rex sole averaged 

 about 3000 t during 1999-2003, ap- 

 proximately 35% of the ABC (Turnock 

 et al.''). The low harvest level may be 

 due, in part, to constraints placed on 



' Turnock. B. J. 2004. Personal commun. 

 Alaska Fisheries Science Center, National 

 Marine Fisheries Service, 7600 Sand 

 Point Way NE. Seattle, WA 98115. 



- Quirollo, L. F., and C. M. Dewees. 2001. 

 California's living marine resources: a 

 status report. California Department 

 of Fish and Game. Website: http:// 

 www.dfg.ca.gov/mrd/status/rex_sole.pdf 

 {accessed on 9 September 2004]. 



^ Spencer, P. D., G. E. Walters, and T. K. 

 Wilderbuer. 2001. Stock assessment 

 and fishery evaluation: Bering Sea other 

 flatfish. Website: http://www.afsc. 

 noaa.gov/refm/docs/2001/BSoflats.pdf 

 [accessed on 13 September 2004]. 



^ DiCosimo, J., and N. Kimball. 2001. 

 Groundfish of the Gulf of Alaska: A 

 species profile. North Pacific Fisheries 

 Management Council Report. Website: 

 http://www.fakr.noaa.gov/npfmc/reports/ 

 goaspecies2001.pdf [accessed on 3 March 

 2003]. 



•-' Turnock, B. J., T. K. Wilderbuer, and 

 E.S.Brown. 2003. Stock assessment 

 and fishery evaluation: Gulf of Alaska 

 flatfish. Website: http://www.afsc. 

 noaa.gov/refm/docs/2003/GOAflats.pdf 

 [accessed on 10 September 2004]. 



